1. Field of the Invention
The present invention relates to a light guide plate and a surface light source unit using the same, and especially to a light guide plate providing highly uniform illumination.
2. Description of Prior Art
Recently, liquid crystal display devices have undergone remarkable improvements, and their market has been steadily growing. These devices save installation space by virtue of their slimness, and they can also save power.
Liquid crystal displays commonly use a surface light source to provide illumination. The surface light source includes a light guide plate having a uniform thickness or being wedge-shaped. The light guide plate distributes light from a substantially linear source such as a cold cathode fluorescent lamp (CCFL), in order to provide substantially even illumination to the LCD.
In particular, the light guide plate is provided for distribution of light from the light source over an area much larger than an area of the light source; that is, over an entire output surface area of the light guide plate. In operation, light beams typically enter the light guide plate at an edge surface thereof. Some of the light beams propagate between a bottom surface and the output surface toward an opposite end surface of the light guide plate by total internal reflection, and other light beams are output through the output surface directly. Further, the bottom surface includes structures such as dots formed thereon or facets cut therein and arranged in a pattern. Light beams that impinge on these structures are diffusely reflected and then emitted through the output surface.
FIG. 4 shows a conventional light guide plate 12, which comprises a light incidence surface 121, an emission surface 122, a bottom surface 123 opposite to the emission surface 122, and a plurality of diffusion dots 124 formed on the bottom surface 123.
FIG. 5 is an enlarged view of part of the light guide plate 12 of FIG. 4. The diffusion dots 124 are formed by a screen printing technique, which employs pale or white ink containing a white pigment 125 such as titanium dioxide (TiO2) or barium sulfate (BaSO4). However, the reflectivity of the white pigment 125 is limited. Furthermore, when light is reflected by the white pigment 125, a part of the light is also absorbed by the white pigment 125. This loss of light beams means that the light guide plate 12 cannot provide high uniform illumination and high brightness for a liquid crystal display panel.
Accordingly, it is desired to provide a light guide plate that solves the above-mentioned problems.